When to Get a CT Scan for Headaches

When to Get a CT Scan for Headaches: Key Considerations

Everyone experiences headaches from time to time, but when should headaches be a cause for concern? There are certain red flags or concerning symptoms for headaches that you should see a healthcare professional about.

So if you’re wondering, “When should I get a CT scan for headaches?”, read on to discover which symptoms are concerning and how imaging tests, such as CT, can help uncover the underlying causes of headaches.

When to see a doctor about headaches

There are well over 100 different types of headache, including tension headaches, cluster headaches and migraines.

Most headaches will go away on their own and do not have a serious underlying cause. However, a severe headache or worsening headache may need to be investigated.

You should seek emergency medical attention if your headache:

gets worse over 24 hours
is sudden and severe – often described as ‘the worst headache ever’ or as causing ‘blinding pain’
happens immediately after a head trauma
comes on straight after physical exertion, such as aerobics, jogging, sex or weightlifting
feels like it’s in and around one eye, which is red

Other symptoms you can get with a headache and mean you should seek emergency medical attention include:

balance problems
confusion
difficulty moving your limbs
vision problems
memory loss
slurred speech

You should see your GP as soon as possible if your headaches interfere with your sleep. This includes headaches that make it difficult to fall asleep or regularly waking up with headaches. You should also see your GP if your headaches are usually worse in the morning, last for more than a few days or often don’t have a known cause.

If you already have a history of headaches, you should see your GP if they change in their severity, when they occur or how often they occur.

Your doctor will ask you about your symptoms and medical history, and may perform a physical examination. Based on your answers and their assessment, they will decide whether your symptoms need further investigation using brain scans.

If brain imaging is needed, a CT scan or MRI scan will be recommended based on your symptoms.

Comparing CT scans and MRI for headaches

What is a CT scan?

A CT scan (computed tomography) uses X rays and computer technology to create detailed, 3D images of the inside of your body.

A CT scanner includes a patient table and a doughnut-shaped ring that contains an X-ray generator, which releases X rays, and an X-ray detector, which picks up X-ray signals.

During a CT scan, you will lie down on the patient table, which will be slid through the ring. X-ray beams will then be passed into your body. Some X rays will be absorbed by your tissues – denser tissues (eg bones) absorb more X rays. Some X rays will pass through your body and will be picked up by the X-ray detector.

These X-ray signals are sent to a computer where they are processed into a 2D cross-section of part of your body. Multiple cross-sectional images are created and processed to form a 3D image.

The most dense tissues appear white on a CT scan, while the least dense areas (eg air, fat and fluid) appear black. All other areas appear varying shades of grey.

What is an MRI scan?

An MRI scan (magnetic resonance imaging) uses strong magnets and radio waves to create detailed images of the inside of your body.

An MRI machine includes a patient table and a tube structure containing powerful magnets and coils that produce radio waves.

During an MRI scan, you will lie down on the patient table, which will be slid into the tube. A magnetic field will be created around you, and gentle pulses of radio waves will be passed through your body. Together, this generates signals from the water molecules in your tissues.

As with a CT scan, these signals are processed to form a 2D image of a cross-section through part of your body. Multiple cross-sectional images are then created and processed into a 3D image.

Tissues that contain more water appear brighter and whiter on an MRI scan, while areas that contain little to no water (eg gaps of air) appear black. All other areas appear lighter or darker grey.

CT scans vs MRI scans for headaches

Both CT and MRI produce highly detailed pictures of soft tissues. However, CT has better spatial resolution, which means it’s good at showing the precise boundaries between different structures. MRI has better contrast resolution, which means it’s good at showing subtle differences within soft tissues in more detail.

As CT scans are faster and more readily available than MRI scans, they are usually the preferred choice in an emergency situation. For example, a head CT scan may be used to investigate a severe, sudden onset headache after strenuous activity, which could be a stroke. Or, it could be used to investigate headaches caused by suspected skull fractures after a traumatic brain injury.

As MRI scans can detect small changes in soft tissues, they are often used to diagnose brain cancer, to assess the extent of damage after a stroke diagnosis and to detect soft tissue changes such as inflammation or infection.

Understanding risks and benefits of CT scans

CT scan risks

The main risk of having a CT scan is radiation exposure. However, the levels of radiation used in a head scan are considered safe. Nonetheless, to avoid unnecessary exposure to radiation, you will need a doctor to determine whether you need a CT scan. This means you can’t self-refer for a CT scan.

CT scan benefits

A head CT scan is relatively quick compared to an MRI scan, taking just 5-10 minutes.

As it provides detailed 3D images, it allows your doctor to get a comprehensive view of your brain and other tissues within your head. This can help quickly diagnose serious medical conditions, such as a haemorrhage (brain bleed) or skull fractures.

Although radiation is used, the levels used are low. A head CT scan exposes you to roughly the same amount of radiation you would be exposed to from your environment over 7 months.

What’s more, during a head CT scan, only the head area needs to pass into the ring of the CT scanner. This means pregnant women can safely have a CT scan despite the use of radiation as the abdominal area is not exposed to the X rays used.

Medical conditions that cause headaches

A headache can be either a primary headache or a secondary headache. In general, primary headaches are not caused by an underlying health condition, while secondary headaches are.

Many primary headaches are caused by lifestyle factors such as a lack of sleep, stress, drinking too much alcohol, not drinking enough fluids, skipping meals, poor posture and eating certain foods (eg foods high in nitrates).

Secondary headaches are caused by an underlying health condition. Some of these health conditions are serious and need an accurate diagnosis with imaging tests such as CT or MRI.

Serious health conditions that can cause secondary headaches include:

a brain tumour
bleeding within the skull (intracranial hematoma)
blood clots in the brain (venous thrombosis)
concussion
infection of the brain linings (meningitis) or brain (encephalitis)
swelling of blood vessels in the brain (brain aneurysm) and stroke

Other conditions that can cause secondary headaches include dental problems, ear infections and infection of your sinuses, which is often caused by the common cold.

Preparing for your CT scan appointment

If you’re having a standard CT scan without contrast material, you can eat, drink and take your medications as normal.

If you are having a CT scan with a contrast agent, your care team will tell you to fast for a certain number of hours before your scan. This means not eating or drinking anything other than water. You will also be asked to remain at the scanning facility after your scan for around 30 minutes to check that you don’t develop an allergic reaction to the contrast agent – this is rare and, in most cases, mild and easily treated.

For a head CT scan, you will not usually need to change into a hospital gown. However, you will be asked to remove any metal items from your body. This is because metal can introduce shadows and streaks on the CT images, which can make an accurate diagnosis more difficult.

During your scan, you will be lying flat on a patient table, which will be slid into the ring part of the CT machine. If you have any anxiety about this procedure, you can bring a friend or family member with you to your appointment. You should also let your care team know so they can better support you.

Do you need a CT scan?

If you’re concerned about persistent headaches or other worrying headache symptoms, our experienced GPs at Vista Health can help.

Simply book a virtual GP consultation to discuss your concerns, and your Vista Health GP will let you know whether you need imaging tests, such as a private CT scan, at one of our conveniently located nationwide clinics.